1. Field of the Invention
The present invention relates to a method of observing patterns using a beam of electrons, and particularly to a method of observing a contact hole using a beam of electrons.
2. Description of Related Art
Japanese Patent Application Laid-open Publication No. 2000-200579 describes a pre-charging method of observing a workpiece by use of an electron microscope by positively charging the surface of the workpiece. In the case of this method, a beam of electrons is irradiated on a wider range in the surface of the workpiece, or a beam of electrons is irradiated on the workpiece with a lower magnification, for the purpose of enhancing the pre-charging effect. Japanese Patent Translation Publication No. 2002-524827 describes a method of continuously observing a workpiece by an alternate series of observations and setups in a case where electrostatic charge in a spot to be observed is changed by a beam of electrons which is irradiated for observing the workpiece or acquiring an image of the workpiece. The setups are performed for controlling a condition in which the spot to be observed is electrostatically charged. To this end, the conditions under which a beam of electrons is irradiated on the spot to be observed are different from the observation conditions. According to this method of continuous observation, the setups and observations need to be carried out alternately and repeatedly. This is because each of the setups performed by irradiating a beam of electrons so that the electrostatic charge of the spot to be observed, which is generated while an image is being acquired, can be offset by the setups